title: Circumferential or sectored beam arrangements for stereotactic body radiation therapy (SBRT) of primary lung tumors: effect on target and normal-structure dose-volume metrics.
abstract: To compare 2 beam arrangements, sectored (beam entry over ipsilateral hemithorax) vs circumferential (beam entry over both ipsilateral and contralateral lungs), for static-gantry intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) delivery techniques with respect to target and organs-at-risk (OAR) dose-volume metrics, as well as treatment delivery efficiency. Data from 60 consecutive patients treated using stereotactic body radiation therapy (SBRT) for primary non-small-cell lung cancer (NSCLC) formed the basis of this study. Four treatment plans were generated per data set: IMRT/VMAT plans using sectored (-s) and circumferential (-c) configurations. The prescribed dose (PD) was 60Gy in 5 fractions to 95% of the planning target volume (PTV) (maximum PTV dose ~ 150% PD) for a 6-MV photon beam. Plan conformality, R50 (ratio of volume circumscribed by the 50% isodose line and the PTV), and D2cm (Dmax at a distance ≥2cm beyond the PTV) were evaluated. For lungs, mean doses (mean lung dose [MLD]) and percent V30/V20/V10/V5Gy were assessed. Spinal cord and esophagus Dmax and D5/D50 were computed. Chest wall (CW) Dmax and absolute V30/V20/V10/V5Gy were reported. Sectored SBRT planning resulted in significant decrease in contralateral MLD and V10/V5Gy, as well as contralateral CW Dmax and V10/V5Gy (all p < 0.001). Nominal reductions of Dmax and D5/D50 for the spinal cord with sectored planning did not reach statistical significance for static-gantry IMRT, although VMAT metrics did show a statistically significant decrease (all p < 0.001). The respective measures for esophageal doses were significantly lower with sectored planning (p < 0.001). Despite comparable dose conformality, irrespective of planning configuration, R50 significantly improved with IMRT-s/VMAT-c (p < 0.001/p = 0.008), whereas D2cm significantly improved with VMAT-c (p < 0.001). Plan delivery efficiency improved with sectored technique (p < 0.001); mean monitor unit (MU)/cGy of PD decreased from 5.8 ± 1.9 vs 5.3 ± 1.7 (IMRT) and 2.7 ± 0.4 vs 2.4 ± 0.3 (VMAT). The sectored configuration achieves unambiguous dosimetric advantages over circumferential arrangement in terms of esophageal, contralateral CW, and contralateral lung sparing, in addition to being more efficient at delivery.
authors.affiliation: Broad Institute of MIT and Harvard, Cambridge, MA; Department of Physics, Brandeis University, Waltham, MA.
authors.forename: Mara W
authors.initials: MW
authors.lastname: Rosenberg
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Kato
authors.forename: Kelly M P
authors.initials: KM
authors.lastname: Carson
authors.forename: Nathan M
authors.initials: NM
authors.lastname: Matsunaga
authors.forename: Robert F
authors.initials: RF
authors.lastname: Arao
authors.forename: Emily J
authors.initials: EJ
authors.lastname: Doss
authors.forename: Charles L
authors.initials: CL
authors.lastname: McCracken
authors.forename: Lu Z
authors.initials: LZ
authors.lastname: Meng
authors.forename: Yiyi
authors.initials: Y
authors.lastname: Chen
authors.forename: Wolfram U
authors.initials: WU
authors.lastname: Laub
authors.forename: Martin
authors.initials: M
authors.lastname: Fuss
authors.forename: James A
authors.initials: JA
authors.lastname: Tanyi
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002289:Carcinoma, Non-Small-Cell Lung / Q000601:surgery*; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D016634:Radiosurgery; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated
keywords: Beam configuration; Intensity-modulated arc therapy; Intensity-modulated radiotherapy; Stereotactic body radiotherapy